DEVELOPMENT OF THE ATOLL 255 



or the growtli of neighbouring colonies, or by the welding ol 

 smaller fragments, will be firmly reseated on their new site. 

 A point on the reef is thus formed upon which the waves will 

 break in ordinary weather. In time the process spreads, and 

 instead of there being only one point upon which waves break, 

 a line of breakers will be formed ; and as the line continues to 

 grow it will become a crescent, tailing off around the edge of the 

 reef. Smoother water will be present within the protecting 

 crescent, and there fragments that have been hurled inwards 

 from the edge will become lodged. These fragments, again, 

 become welded by the deposition of the calcium carbonate 

 around the particles driven among them, and the breccia 

 masses tend to become a continuous rampart. Waves will 

 break upon the boulder-piled edge and sweep across this 

 rampart, and, as they do so, will become spent : — there will 

 therefore be a tailing off of the breccia layer within, and we - 

 may expect to find sand and sediment deposited in such a 

 way as to build up a shore internal to the platform. With 

 the perpetual sweep of waves across the platform, and the 

 constant addition of new fragments and the deposition of 

 calcium carbonate, the whole becomes levelled, or approxi- 

 mately levelled ; its completed stage will be that of a uniform 

 concrete platform, ending sheer at its outer edge, and tailing 

 off" as a debris slope within. The level it assumes will be 

 that of the point of the maximum intensity of wave action 

 at all tides. When the tide is low the waves will crash upon 

 the outer edge and move large masses of rock in times of 

 storm ; but as the tide rises the surf-line sweeps on across the 

 fiats and rushes with decreasing force to their inner edge. At 

 high tide, therefore, smaller fragments will be swept across the 

 flats and be left there with the fall of the tide, so that the 

 inner edge becomes raised. The intermediate part will bear 

 the full brunt of the surf during the rising and the falling of 

 the tide, and so it will become the most levelled by wave 

 action. The outer margin will receive the first force and the 

 great lifting power of the ocean waves, and so will become the 

 site of the biggest of the masses that the waves may lift and 



